U.S. patent application number 10/169379 was filed with the patent office on 2003-05-15 for fuel injection system for internal combustion engines exhibiting improved start behavior.
Invention is credited to SCHUELER, Peter.
Application Number | 20030089341 10/169379 |
Document ID | / |
Family ID | 7663786 |
Filed Date | 2003-05-15 |
United States Patent
Application |
20030089341 |
Kind Code |
A1 |
SCHUELER, Peter |
May 15, 2003 |
Fuel injection system for internal combustion engines exhibiting
improved start behavior
Abstract
A fuel injection system is proposed, in which, by means of a
controlled zero-feed throttle (49) or by the elimination of the
zero-feed throttle and by a suitable control of the pressure valve
(51) of a common rail (25), the starting performance of the
internal combustion engine can be improved, and at the same time it
is assured that in the overrunning mode of the engine, an
excessively high pressure is not built up in the common rail.
Inventors: |
SCHUELER, Peter; (Leonberg,
DE) |
Correspondence
Address: |
RONALD E. GREIGG
GREIGG & GREIGG P.L.L.C.
1423 POWHATAN STREET, UNIT ONE
ALEXANDRIA
VA
22314
US
|
Family ID: |
7663786 |
Appl. No.: |
10/169379 |
Filed: |
September 30, 2002 |
PCT Filed: |
November 16, 2001 |
PCT NO: |
PCT/DE01/04317 |
Current U.S.
Class: |
123/458 ;
123/446; 123/457; 417/279 |
Current CPC
Class: |
F02M 63/025 20130101;
F02M 59/34 20130101; F02M 63/0001 20130101 |
Class at
Publication: |
123/458 ;
123/457; 123/446; 417/279 |
International
Class: |
F02M 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 18, 2000 |
DE |
100 57 244.8 |
Claims
1. A high-pressure fuel pump for a fuel injection system of an
internal combustion engine, having at least one pump element (19),
having a prefeed pump (1), having a metering valve (47), the
prefeed pump (1) pumping fuel from a tank (5) to the suction side
of the pump element or elements (19), and the fuel quantity pumped
by the prefeed pump (1) to the suction side of the pump element or
elements (19) being regulatable by the metering valve (47), and
having a throttle (49) for limiting the fuel outflow from the
suction side of the pump element or elements (19), characterized in
that the throttle (49) is controllable.
2. The high-pressure fuel pump of claim 1, characterized in that
the throttle (49) closes when the fuel pressure on the compression
side (15) of the prefeed pump (1) is below a first reference
value.
3. The high-pressure fuel pump of claim 1 or 2, characterized in
that the throttle (49) is controlled by a control valve (55) that
is subjected to the fuel pressure on the compression side (15) of
the prefeed pump (1).
4. The high-pressure fuel pump of claim 3, characterized in that
the control valve (35) also controls the inflow of fuel into the
high-pressure fuel pump for the sake of lubrication.
5. The high-pressure fuel pump of claim 4, characterized in that
the control valve (35) is a cascade valve, and that the control
valve (35) controls the inflow of fuel into the high-pressure fuel
pump (17) for the sake of lubrication in a plurality of stages.
6. The high-pressure fuel pump of one of claims 3-5, characterized
in that the throttle (49) is integrated with the control valve (55,
35).
7. The high-pressure fuel pump of one of the foregoing claims,
characterized in that the throttle (49) communicates on the outlet
side with a return line (29) that discharges into the tank (5).
8. The high-pressure fuel pump of one of claims 1-6, characterized
in that the throttle (49) communicates on the outlet side with an
inlet line (3) of the prefeed pump (1).
9. The high-pressure fuel pump of one of claims 1-6, characterized
in that the throttle (49) communicates on the outlet side with the
lubrication of the high-pressure fuel pump (17).
10. A fuel injection system for an internal combustion engine,
having a high-pressure fuel pump (1), wherein the high-pressure
fuel pump (17) has at least one pump element (19), having a prefeed
pump (1), having a metering valve (47), wherein the prefeed pump
(1) pumps fuel from a tank (5) to the suction side of the pump
element or elements (19), and the fuel quantity pumped by the
prefeed pump (1) to the suction side of the pump element or
elements (19) is regulatable by the metering valve (47), having a
common rail (25) communicating with the compression side of the
high-pressure fuel pump (17), wherein the common rail (25) can be
made to communicate with a fuel return (29) via a pressure
regulating valve (51), characterized in that in the overrunning
mode of the engine, the pressure regulating valve (51) is opened
and the metering valve (47) is closed.
11. The fuel injection system of claim 10, characterized in that
the pressure valve (51) is a blocking or flow valve.
12. The fuel injection system of claim 10 or 11, characterized in
that a control unit is provided for controlling the fuel injection
system.
13. The high-pressure fuel pump of one of the foregoing claims,
characterized in that the prefeed pump (1) is a geared pump, and
that the prefeed pump (1) is driven by the high-pressure fuel pump
(17) or by the engine.
Description
[0001] The invention relates to a high-pressure fuel pump for a
fuel injection system of an internal combustion engine, having at
least one pump element, having a prefeed pump, having a metering
valve, the prefeed pump pumping fuel from a tank to the suction
side of the pump element or elements, and the fuel quantity pumped
by the prefeed pump to the suction side of the pump element or
elements being regulatable by the metering valve, and having a
throttle for limiting the fuel outflow from the suction side of the
pump element or elements, and to a fuel injection system as
generically defined by the preamble to the coordinate claim 10.
PRIOR ART
[0002] For regulating the pumping quantity of a high- pressure fuel
pump, a metering valve is disposed on the suction side of the pump
elements of the high-pressure fuel pump and brings about a more or
less pronounced throttling.
[0003] In the overrunning mode of the engine, or when a motor
vehicle is moving downhill, fuel should not be injected into the
combustion chambers of the engine. For this reason, in the
overrunning mode the metering valve is closed. Since even in the
closed state the metering valve has a certain leakage, even in the
overrunning mode some quantity of fuel, although slight, reaches
the pump elements and is aspirated by them. The fuel pumped by the
pump elements, which is at high pressure, flows for instance into
the common rail of the fuel injection system, and it can
accordingly cause an undesirably high pressure to be built up in
the overrunning mode, since the injectors are not injecting any
fuel into the combustion chambers.
[0004] To prevent this, it is known to provide a so-called
"zero-feed" throttle, through which small quantities of fuel can
flow from the suction side of the pump elements out into a fuel
return or to the suction side of the prefeed pump. This prevents a
pressure from building up on the suction side of the pump elements
and thus prevents the pump elements from being able to overcome the
closing force of the suction valves. Consequently in the
overrunning mode the pump elements aspirate no fuel, and the
unwanted buildup of pressure in the common rail during the
overrunning mode is averted.
[0005] A disadvantage of this provision is that the zero-feed
throttle is opened even upon starting of the engine, and thus the
pressure buildup on the suction side of the pump elements is
delayed or more difficult. Consequently the engine requires a high
starting rpm and does not start until after a certain amount of
time.
[0006] The object of the invention is to furnish a high-pressure
fuel pump for a fuel injection system, as well as a fuel injection
system, for an internal combustion engine, which when they are used
improve the starting performance of the engine.
[0007] This object is attained according to the invention by a
high-pressure fuel pump for a fuel injection system of an internal
combustion engine, having at least one pump element, having a
prefeed pump, having a metering valve, the prefeed pump pumping
fuel from a tank to the suction side of the pump element or
elements, and the fuel quantity pumped by the prefeed pump to the
suction side of the pump element or elements being regulatable by
the metering valve, and having a controllable throttle for limiting
the fuel outflow from the suction side of the pump element or
elements.
ADVANTAGES OF THE INVENTION
[0008] In the high-pressure fuel pump of the invention, the
throttle can be closed during starting, so that the pressure
buildup on the suction side of the pump elements is completed
faster and the starting performance of the engine is thus
improved.
[0009] In a variant of the invention, it is provided that the
throttle closes when the fuel pressure on the compression side of
the prefeed pump is below a first reference value, so that in all
operating states in which the fuel supply to the high-pressure fuel
pump is inadequate, the throttle is closed, and hence the entire
amount of fuel pumped by the prefeed pump is available to the pump
elements.
[0010] In a further feature of the invention, the throttle is
controlled by a control valve that is subjected to the fuel
pressure on the compression side of the prefeed pump, so that the
control of the throttle is accomplished in a simple, reliable way.
A control unit of the fuel injection system is not needed for this
purpose.
[0011] In a further refinement of the invention, it is provided
that the control valve also controls the inflow of fuel into the
high-pressure fuel pump for the sake of lubrication, so that both
functions, namely the control of the throttle and of the inflow of
fuel into the high-pressure fuel pump for lubrication, can be
accomplished simply and economically with one valve.
[0012] In a further feature of the invention, it is provided that
the control valve is a cascade valve, and that the control valve
controls the inflow of fuel into the high-pressure fuel pump for
the sake of lubrication in a plurality of stages, thus on the one
hand assuring that the high-pressure fuel pump is always adequately
lubricated and on the other that there is enough fuel available to
the pump elements at low rotary speeds.
[0013] It is especially advantageous if the throttle is integrated
with the control valve, so that the number of component groups and
connecting lines required is less, and less space is needed.
[0014] Further features of the invention provide that the throttle
communicates on the outlet side with a return line that discharges
into the tank, or with the suction side of the prefeed pump, or
with the lubrication of the high-pressure fuel pump, so that
regardless of how the throttle is connected on the outlet side, the
advantages of the invention can be exploited.
[0015] The object stated above is also attained according to the
invention by a fuel injection system for an internal combustion
engine, having a high-pressure fuel pump, wherein the high-pressure
fuel pump has at least one pump element, having a prefeed pump,
having a metering valve, wherein the prefeed pump pumps fuel from a
tank to the suction side of the pump element or elements, and the
fuel quantity pumped by the prefeed pump to the suction side of the
pump element or elements is regulatable by the metering valve,
having a common rail communicating with the compression side of the
high-pressure fuel pump, wherein the common rail can be made to
communicate with a fuel return via a pressure regulating valve, and
wherein in the overrunning mode of the engine, the pressure
regulating valve is opened and the metering valve is closed.
[0016] In this fuel injection system, a zero-feed throttle can be
dispensed with, since in the overrunning mode the pressure
regulating valve is opened, and thus the pressure in the common
rail drops so far that a pressure buildup in the overrunning mode
is impossible. The fuel quantity pumped by the high-pressure fuel
pump in the overrunning mode is equivalent to the leakage from the
metering system and is very slight. An especially advantageous
feature of the fuel injection system of the invention is that the
function of the zero-feed throttle is achieved by means of a
suitable triggering of the pressure valve that is present anyway
and the metering valve that is also present anyway. This simplifies
the structure of the fuel injection system and enhances its
reliability.
[0017] In other features of the fuel injection system, it is
provided that the pressure valve is a blocking or flow valve,
and/or that a control unit is provided for controlling the fuel
injection system, so that depending on the concept of regulation in
the fuel injection system, the pressure in the common rail can be
controlled by a blocking valve or a flow valve.
[0018] In another embodiment of the invention, the prefeed pump is
a geared pump, and that the prefeed pump is driven by the
high-pressure fuel pump or by the engine. Since in high-pressure
fuel pumps of this design, the rpm and thus the pumping capacity of
the prefeed pump depend directly on the rpm of the engine, the
pressure buildup on the suction side of the pump elements upon
engine starting proceeds relatively slowly, so that the advantages
of the high-pressure fuel pump of the invention and of the fuel
injection system of the invention are especially advantageously
attained.
[0019] Further advantages and advantageous features of the
invention can be learned from the accompanying drawing and its
description.
DRAWING
[0020] Shown are:
[0021] FIG. 1, a fuel injection system of the prior art;
[0022] FIGS. 2-5, exemplary embodiments of fuel injection systems
of the invention; and
[0023] FIG. 8, a graph from which the advantages of the fuel
injection system of the invention are demonstrated.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0024] In FIG. 1, a common rail injection system of the prior art
is shown schematically. A prefeed pump 1, via an inlet line 3,
aspirates fuel, not shown, from a tank 5. The fuel is filtered in a
prefilter 7 and a filter with a water trap 9.
[0025] The prefeed pump 1 is embodied as a geared pump and has a
first overpressure valve 11. On the suction side, the prefeed pump
is throttled by a first throttle 13. A compression side 15 of the
prefeed pump 1 supplies fuel to a high-pressure fuel pump 17. The
high-pressure fuel pump 17 is embodied as a radial piston pump,
with three pump elements 19, and it drives the prefeed pump 1. One
suction valve 21 is provided on the suction side of each of the
pump elements 19. One check valve 23 is provided on the compression
side of each of the pump elements 19 and prevents the fuel, which
is at high pressure and has been pumped into a common rail 25 by
the pump elements 19, from being able to flow back into the pump
elements 19.
[0026] The high-pressure lines of the fuel injection system are
represented by heavy lines in FIGS. 1 through 5, while the regions
of the fuel injection system that are at a low pressure are
represented by fine lines.
[0027] The common rail 35 supplies one or more injectors, not shown
in FIG. 1, with fuel via a high-pressure line 27. A second
overpressure valve 28, which as needed connects the common rail to
a return line 29, prevents excessively high pressures in the
high-pressure region of the fuel injection system. Via the return
line 29 and a leakage line 31, the leakage and the control
quantities for the injector or injectors, not shown, are returned
to the tank 5.
[0028] Via a switching valve 33, the fuel located in the return
line 29 can also be transported into the inlet line 3 of the
prefeed pump 1, so that the risk of gelatinization at low
temperatures is reduced.
[0029] The high-pressure fuel pump 17 is supplied by the prefeed
pump 1 with fuel for the pump elements 19 on the one hand and fuel
for lubrication on the other. The fuel quantity used for
lubricating the high-pressure fuel pump 17 is controlled via a
first control valve 35 and a second throttle 37. In the position
shown in FIG. 1 for the first control valve 35, the pressure on the
compression side 15 of the prefeed pump 1 is note sufficient to
move a piston 39 of the first control valve 35 counter to the
spring force of a spring 41. As a consequence, the first control
valve 35 is shown closed in FIG. 1. As soon as the pressure on the
compression side 15 rises, the piston 39 moves to the left counter
to the spring force of the spring 41 and opens the line 43. Via the
line 43 and the second throttle 37, flow for lubricating the
high-pressure fuel pump 17 flows into the crankcase of this
pump.
[0030] Via a distribution line 45, the high-pressure fuel pump 17
also supplies the pump elements 19 with fuel. For regulating the
pumping quantity of the high-pressure fuel pump 17, a metering
valve 47 is provided between the compression side 15 of the prefeed
pump 1 and the distribution line 45. The metering valve 47 is a
flow valve, which is triggered by a control unit, not shown, of the
fuel injection system. The pump elements 19 are thus throttled on
the suction side via the metering valve 47.
[0031] In the overrunning mode, that is, when a vehicle is
travelling downhill, for instance, no fuel is supposed to flow into
the pump elements 19, and accordingly no fuel is to be injected by
the injectors, not shown, into the combustion chambers of the
engine. Since for production and functional reasons the metering
valve 47 in the closed state still has a leakage quantity that
flows into the distribution line 45, a pressure would build up on
the suction side of the pump elements 19, unless suitable remedies
are provided, that would be so high that the pump elements would
open the suction valves 21 during the intake stroke and would
aspirate fuel. The consequence would be that the pressure in the
common rail 25 would rise excessively.
[0032] To prevent this, a third throttle 49 is provided, which will
hereinafter also be called a zero-feed throttle. Through the
zero-feed throttle 49, the fuel can flow out of the distribution
line 45 into the crankcase of the high-pressure fuel pump 17, where
it can be used to lubricate the high-pressure fuel pump 17. Because
of the outflow of fuel through the zero-feed throttle 49, the
aforementioned pressure buildup in the distribution line 45 in the
overrunning mode resulting from leakage from the closed metering
valve 47 is averted.
[0033] A disadvantage of this provision is that the zero-feed
throttle 49 is always open, and thus especially at low rpm, of the
kind that occurs when the engine is started, the desired pressure
buildup in the distribution line 45 is prevented by the outflow of
fuel through the zero-feed throttle 49.
[0034] The pressure in the common rail 25 is regulated via a
pressure valve 51, which can also be embodied as a flow valve. The
pressure valve 51 is likewise triggered by the control unit, not
shown.
[0035] In FIGS. 2 through 5, various embodiments according to the
invention for a fuel injection system are shown; for identical
components, the same reference numerals are used, and reference can
be had to the description of FIG. 1.
[0036] In FIG. 2, the first control valve 35 is connected parallel
to a fourth throttle 53, serving to ventilate the system, so that
with the onset of pumping by the prefeed pump 1, fuel for
lubrication also reaches the high-pressure fuel pump 17. In this
exemplary embodiment, the zero-feed throttle 49 connects the
distribution line 45 with the return line 29. The flow through the
zero-feed throttle 49 is controlled by a second control valve 55.
The second control valve 45 has a piston 57, which is subjected to
the pressure of the compression side of the prefeed pump 1. If the
pressure on the compression side 15 is low, a ball 59 is pressed by
a spring 61 into a sealing seat 63 and thus closes the second
control valve 55. As soon as the pressure on the compression side
15 of the prefeed pump 1 exceeds a first reference value, the
piston 47 moves to the left and via a pin 63 lifts the ball 61 from
its seat, and thus opens the second control valve. As a result, the
control valve 55 means that in the starting process the pressure
buildup in the distribution line 45 is speeded up, since no fuel is
flowing out through the zero-feed throttle 49. The high-pressure
fuel pump 17 consequently begins to pump earlier, the pressure
buildup in the common rail 25 is speeded up, and the engine begins
to work earlier and at lower rpm levels.
[0037] If the motor is in the overrunning mode, that is, if it is
operating at a higher rpm than idling but with a closed metering
valve 47, the pressure on the compression side 15 of the prefeed
pump is high enough to open the second control valve 55 and thus to
assure the above-described function of the zero-feed throttle 49.
This is especially advantageous if the prefeed pump 1 is driven
directly by the high-pressure fuel pump 17, since in that case the
rpm of the engine, of the high-pressure fuel pump, and of the
prefeed pump 1 are coupled directly to one another.
[0038] In the exemplary embodiment of FIG. 3, the control of the
zero-feed throttle 49 is integrated with the first control valve
35. The first control valve 35 is embodied as a cascade valve; that
is, the fuel for lubricating the high-pressure fuel pump 1, given
an only slight pressure on the compression side 15 of the prefeed
pump 1, can flow through the fourth throttle 53, serving to
ventilate the system, into the crankcase of the high-pressure fuel
pump 17. As soon as the pressure on the compression side 15 of the
prefeed pump 1 exceeds a first reference value, the first control
valve opens and uncovers a third throttle 65, which is connected
parallel to the fourth throttle 53. Thus the fuel flow furnished
for lubricating the high-pressure fuel pump 17 is increased, which
is necessary especially at relatively high rpm of the high-pressure
fuel pump 17 and thus also of the prefeed pump 1. Once the first
reference value on the compression side 15 is reached, the
zero-feed throttle 49 is also opened through an opening in the
piston 39 of the first control valve 35. Via a leakage drain 67 of
the first control valve, fuel, which has reached the first control
valve 35 from the distribution line 45 via the zero-feed throttle
49, is drained away and used to lubricate the high-pressure fuel
pump 17.
[0039] It is also possible for the opening of the zero-feed
throttle 49 and of the fifth throttle 65 takes place at different
pressures on the compression side 15 of the prefeed pump 1. In the
exemplary embodiment of FIG. 4, the first control valve 35 is again
embodied as a cascade valve. The piston 39 of the first control
valve 35 has an annular groove 69, which when a first reference
value on the compression side 15 of the prefeed pump 1 is attained
is located such that the zero-feed throttle 49 communicates with an
outlet line 71. The outlet line 71 discharges into the inlet line 3
of the prefeed pump 1.
[0040] In the exemplary embodiment of FIG. 5, there is no zero-feed
throttle 49. The first control valve 35 supplies the high-pressure
fuel pump 17 with fuel for lubrication in the manner described
above, while the pump elements 19 are supplied with fuel via the
distribution line 45. Upon starting of the engine, the pressure
valve 51, which is also responsible for regulating the pressure in
the common rail 25, is closed. The pressure buildup in the
distribution line 45 takes place just as fast, since there is no
zero-feed throttle 49, as in the exemplary embodiments of FIGS. 2
through 4, in which the zero-feed throttle 49 is closed during
starting. Since the first control valve 35 is embodied as a cascade
valve, ventilation of the inlet line 3, prefeed pump 1 and
compression side 15 of the prefeed pump 1 can be effected through
the fourth throttle 53, which has a very small cross section.
[0041] In the overrunning mode of the engine, the metering valve 47
is closed. The leakage quantity from the metering valve 47 flows
into the distribution line 45 and reaches the pump elements 19, as
soon as the pressure in the distribution line 45 is high enough and
the pump elements 19 can open the suction valves 21 during the
intake stroke. Since the pressure valve 51 is opened during the
overrunning mode, the pressure in the common rail 25 is not high,
as it is in FIG. 1; on the contrary, a low pressure prevails
through the entire injection system. Consequently, the pumping work
of the pump elements 19 is slight, and the pressure in the common
rail 25 is so slight that the injectors (not shown) do not open,
since the fuel pressure is not sufficient to overcome the closing
force of the nozzle spring of the injectors. In other words, as a
result of the triggering according to the invention of the metering
valve 47 and the pressure valve 51, it is possible to dispense with
a zero-feed throttle 49 without sacrifices in terms of the function
of the fuel injection system.
[0042] For clear illustration of the advantages of the fuel
injection system of the invention, FIG. 6 shows a graph in which a
flow rate 73 is plotted over an rpm n. A first line 75 represents
the pumping quantity of the prefeed pump 1 as a function of the rpm
n. A second line 77 shows the fuel demand of a high-pressure fuel
pump 1 in the prior art. The fuel demand of the high-pressure fuel
pump 1 in the prior art is essentially composed of the
rpm-dependent pumping quantity of the pump elements 19 and the
differential-pressure-dependent volumetric flow through the
zero-feed throttle 49. At the intersection 79 between the first
line 75 and the second line 75, the starting rpm of an internal
combustion engine equipped with a fuel injection system of the
prior art is attained. In the present example, this starting rpm is
133 revolutions per minute.
[0043] A third line 81 represents the fuel demand of an internal
combustion engine equipped with a fuel injection system according
to the invention. The rpm-dependent fuel demand 81 of the
high-pressure fuel pump 17 of the invention depends only on the
pumping quantity of the pump elements 19, and thus over the entire
rpm range it is less than the fuel demand of an internal combustion
engine of the prior art (see second line 77). Consequently, the
intersection 83 between the third line 81 and the first line 75 is
reached at a lower rpm. In the example of FIG. 6, the starting rpm
of an internal combustion engine equipped with the fuel injection
system of the invention is 116 revolutions per minute. In other
words, the engine starts faster; the starter and the on-board
electrical system are burdened less; and starting is still possible
even under less-favorable ambient conditions.
* * * * *